Wallabies work on case for the defence

Australia can't afford to rely on their sensational scrambling defence to bail them out against a rampant All Blacks line-up in Saturday's Rugby World Cup final, they've been warned.

The Wallabies have built their World Cup campaign on remarkable defensive efforts - notably when their 13-man defensive line withheld Wales' attack for seven minutes in their crucial final pool game.

Of the five tries they've conceded this World Cup, three came in their quarter-final escape against Scotland - one from an intercept pass and a second from a charge-down recovery.

But when it comes to conceding tries from open play, only England's Anthony Watson and Fijian five-eighth Ben Volavola have breached the Wallabies' tryline this World Cup.

Argentina made 18 clean breaks in their semi-final loss to Australia, but were repeatedly denied by scrambling cover defence - with five-eighth Bernard Foley regularly called on to make key tackles in the back-field.

But with New Zealand boasting the power-running of Ma'a Nonu, and offloading brilliance of Sonny Bill Williams coming off the bench, Australia can't afford to let attackers shred their edge defence.

"That's right. We're trying to stop things from the start," lock Rob Simmons said.

"We don't have to always be scrambling. If we can nip it in the bud from the start, then we'll try and fix it there."

Nathan Grey is the man tasked with tweaking the Australian defence, but captain Stephen Moore said there was no secret behind his developing a near-impenetrable line.

"It's having a clear plan and going out and doing it for each other and we've spent a lot of time on that," Moore said.

"Working hard for each other and that's important particularly when you're under the pump in big games.

"That's going to be the case at times on the weekend so, once again, we'll have a plan in place and we've got to go out there and be able to execute it under pressure."